This invention relates to the stabilization of polyvinyl chloride resins. More particularly, this invention pertains to the stabilization of polyvinyl chloride resins from the degradative effects of ultraviolet light and heat, as well as improving plate-out resistance.
It is well known that polyvinyl chloride containing resins degrade at elevated temperatures. When vinyl chloride polymers and copolymers are subjected to molding temperatures in excess of about 150.degree. C, they tend to discolor. Serious discoloration occurs even in the relatively short period of time required for a molding operation. This serious coloration of the resin causes a high molded article rejection rate when clear articles are being produced, and further obviates the reuse of scrap material from the molding processes.
In regard to ultraviolet degradation, this takes place subsequent to molding and while the article is in use. Molded polyvinyl chloride panels which are used in exterior construction are particularly susceptible, as well as molded articles such as playground and other recreational equipment, automobile parts and so on, which are exposed to sunlight for long periods of time. Such articles on ultraviolet degradation become embrittled and readily crack or shatter. When this embrittling occurs, the article is no longer effective in its original function.
By plate-out resistance is meant the resistance to forming residual deposits on machine parts such as extruder dies or calender or mill rolls as the resin is being processed. Such deposits left on the rollers will cause imperfections in resin subsequently passed through such rolls. This is a problem particularly in forming films. Unexpectedly, the unactivated Zeolite A and related unactivated naturally occurring molecular sieves increase the plate-out resistance properties of the resin.
This invention is specifically directed to the solving of these related problems. To date, numerous stabilizers have been suggested for use in polyvinyl chloride type resins. The most satisfactory of these stabilizers comprise barium, tin, lead and cadmium containing organometallic compounds. These compounds, while performing satisfactorily, still have not solved the problem of heat and ultraviolet light degradation of polyvinyl chloride resins. In heat stabilization, there is a need for further increasing both the temperature which the resin can withstand as well as the time duration at elevated temperatures. The present invention has to a degree solved this problem by extending both of these barriers. Further, the stabilizer system of the present invention has also proven to increase manyfold the ultraviolet stability of the resin. The increased light stability has now made polyvinyl chloride resins useful for many long term exterior uses.
In essence, the present invention comprises the synergistic stabilizing effect of unactivated Zeolite A type molecular sieves. When used in admixture with these or related conventional polyvinyl chloride stabilizers, there is a synergistic stabilizing effect. This effect is exhibited in higher and longer duration heat stabilities, as well as improved long term ultraviolet light stability.
The prior art is replete with inorganic, organometallic, and organic polyvinyl chloride stabilizer materials. The prior art has also disclosed the use of activated Zeolite A alone as a stabilizer for polyvinyl chloride resins. Such a use for activated Zeolite A is disclosed in U.S. Pat. No. 3,245,946. However, the use of an unactivated Zeolite A, and further, the use of an unactivated Zeolite A in conjunction with an inorganic, organometallic or organic stabilizer has not been disclosed or suggested by the prior art, which has instead directed that Zeolite A molecular sieves not be used. This is for the reason that they contain absorbed water which, by theory, on contact with any chlorine from the polyvinyl chloride resin degradation, would combine to form hydrogen chloride. Hydrogen chloride is known to catalytically aid polyvinyl chloride degradation. However, this water bound in the sieve by adsorbtion is not deleterious, but by some unknown mechanism unexpectedly aids in the transport and trapping of the hydrogen chloride within the sieve. And when this sieve is used in conjunction with the conventional organometallic or organic stabilizers, there is a distinct increase in thermal and light stability.
It is, therefore, a particular object of this invention to set out synergistic polyvinyl chloride stabilizing systems comprised of unactivated Zeolite 3A, unactivated Zeolite 5A, or unactivated Zeolite 4A and conventional inorganic, organic or organometallic stabilizers or mixtures of these stabilizers.
It is further an object of this invention to provide polyvinyl chloride resins which can withstand higher molding temperatures for longer periods of time.
It is also an object of this invention to provide polyvinyl chloride resins which are highly resistant to long term ultraviolet light initiated degradation.
It is additionally an object of this invention to set out polyvinyl chloride resins of increased plate-out resistance.